DNA transcription

Transcription is the process by which information in DNA is transcribed into RNA 

In prokaryotes - DNA simply has coding region, initiator sites and terminator sites where as in eukaryotes the coding region is split into introns (coding regions) and exons (non coding regions) 

The first step of transcription is the interaction of polymerases with the promoter region. The promoter region is a particular sequence upstream of the transcripton initiator site. Polymerases interact with the promoter sequence to unwind the DNA strand. However, in porkaryotes the core enzyme of the polymerase cannot regonise the promoter sequence alone. As a result sigma subunits are invovled. The sigma factors regonise particular sequences such as the -10 and -35 with some variation. They bind slightly upstream of the initator site which enables polymerase to bind. Additionally the sigma factors ensure the polymerase is correctly positioned by placing the polymerase active site in the right location. This enables RNA synthesis to take place by RNAP adding complementary NTP`s at the +1. Once RNA synthesis has begun the sigma factor dissociates. RNA synthesis however, continues until an appropriate termination…